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I have a 15x8 shed that I'm in the process of insulating. The floor appears to be plywood nailed to the joists.

I don't have access to a jack and I'm unable to fit underneath the shed. It appears the plywood goes "underneath" the shed walls if that makes sense. So I'm not sure I will be able to crowbar the floor up and out.

I'd prefer not to place a new floor on top of the existing one as there's not much space already. What are my options here?

I have access to most woodworking tools (i.e. jigsaw, circular saw, etc.)

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    IMHO, unless you live in a really cold area, you aren't going to have much heat loss thru the floor. Since you are insulating, I'm assuming you plan on spending some time there, maybe home office? what floor coverings are you planning...or just leave it plywood? A large throw rug would go a long way in insulating. If you really want to insulate the floor, about the only choice you have is to cut it along the walls and pry up the plywood and insulate it, but beware, there may be some collateral damage in doing so.
    – George Anderson
    Aug 29, 2022 at 21:40
  • If those are standard 8ft walls, can try this answer and lose a couple of inches. diy.stackexchange.com/questions/11740/…
    – crip659
    Aug 29, 2022 at 21:52
  • @GeorgeAnderson there can be some loss depending on the location and climate (and therefore average soil temperature), and an associated discomfort (that's where your feet hang out after all). Topic starter: is any of this the case?
    – MiG
    Aug 29, 2022 at 22:05
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    @GeorgeAnderson I live in Boston so winters can be pretty cold :) That being said I'm using this for my woodworking so I just want to prevent my tools from getting rusted during the humidity changes throughout the seasons in addition to retaining some heat when I use a space heater in the winter.
    – SBT23434
    Aug 30, 2022 at 1:15
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    @SBT23434 Gotcha. I too have a woodworking shop and at times have had to deal with rusting tools. Not fun! Two hints: keep the temp in the shed above outdoor temps and second, get a dehumidifier, preferably one that has a drain hose connection that you can route to the outside so you don't have to worry about constantly emptying a bucket. It made a world of difference in my shop with the added benefit of keeping my wood at a decent moisture content. Yeah, Boston area can get very humid. I've been there and felt like I could cut up the air in 1 foot cubes and carry it with me! LOL
    – George Anderson
    Aug 30, 2022 at 2:58

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Depending what you are insulating it to do in there, laying stuff on top is the most practical, even if you don't want to.

At the low end, carpet pad and carpet (which, of course, does not work well for some uses, but does for others, and is far more insulated than a bare floor, while being easily reversed or removed for upgrade later.) Might only amount to R3, but when you're starting from R1, a total of R4 is a lot better than leaving it at R1.

An inch of foam and 1/4" of underlayment plywood could get you to R7 or R8 in in inch and a quarter of headroom lost with a smooth hard surface, if carpet won't suit the unspecified use.

"Access to a jack" (suitable for a small shed - no need for massive house jacks) is as simple as currently less money than a sheet of plywood costs, perhaps even less if you can focus your working time to fit a tool rental schedule. They are not unobtainable things that you either have, or never will have. They can be rented, or bought and then sold. Or you can very likely borrow the one in your vehicle.

The ply probably was laid on the platform before the walls went up. If you want to go through prying it up, you just cut it at or near the wall line to deal with that, and screw it back down when done. That may require some additional framing support where the walls are parallel to the joists, or you can deliberately leave enough extra wood when cutting to allow splicing it with a backer screwed to both sides of the cut line under the floor.

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    Thanks for your reply, I'm using this for my woodworking shop so my primary goal is to prevent tool rust from the humidity changes. I also want to help it retain heat in the winters while I run a small space heater. Regarding the rust, I've had my tools stored in the shed as-is for a year and have not noticed any. This is mainly precautionary as I'm upgrading to a few nicer tools and would like to preserve them.
    – SBT23434
    Aug 30, 2022 at 1:17
  • A 6-ton hydraulic bottle jack can be had from my local big-box store for under $40. A hydraulic floor jack (for a car) can be had for around $100-$200 (depending on quality and features) and has the added benefit of being able to reuse it for jacking up the car for maintenance. Of course, the bigger issue is getting it jacked high enough to shimmy under without tipping it (brace with 2x4s at an angle on the other side), and in supporting it with some sort of jack stands because you don't want to be under it should the hydraulics fail.
    – FreeMan
    Aug 30, 2022 at 14:39
  • Standard for building jacking is "cribbing" of wood beams. Jack a bit, crib it, set it down, move the jack, jack a bit there, crib it, set it down, move the jack, rinse and repeat until it's as high as you like and set on stable cribbing, not jacks or wobbly jackstands. Don't try to get all the height at one spot at once - you want to keep it close to level as you jack it.
    – Ecnerwal
    Aug 30, 2022 at 15:45

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